Is this better than jump leads ?

Presumably you would prefer the expression negative-chassis then - a metal mounting for the circuit components of an electronic device ? Agreed it makes sense when you say it like that.

Andy

It's common in electronics too - even where the chassis is totally isolated. Ground is of course the correct name. Which can mean earth too. ;-)

However, it doesn't necessarily refer to the negative - just chassis connection.

But only usually with a balanced power supply?

ROFLMAO. Clueless...

Indeed you are, not quite sure why you find it so funny though.

An alternator does indeed produce alternating current (hence the name), which is rectified to produce DC, then regulated to ~14V.

Also true (but slightly unrelated) is the fact that the battery acts as a great big capacitor to smooth out any spikes in voltage.

REGULATED. And the point of a regulator is?

Where does this magical electronics destroying spike in the voltage come from?

Tim.

To (attempt to) regulate the voltage. They aren't perfect though.

Poor regulation (see above). Inductance (e.g. back emf from motors). Transients when switching large loads on and off. Leakage/induced voltage from electronic ignition.

And on, and on, and on... voltage spikes in cars are not exactly rare. The voltage regulator will attempt to filter these out, but it only has a limited capacity to do so. It will not be as effective as the battery.

But certainly not bad enough to do any harm by jump starting the car with the battery disconnected.

Well no it wouldn't because it's connected to the other vehicles battery.

The regulator has a very low impedance load sitting across it normally - the battery. Remove that and anything can happen. Don't think any of them have crowbar protection.

An alternator without the battery could reach very high voltages as the regulator depends on battery voltage. Voltage regs in things like the ECU will probably be ok up to some 30 volts or so. Other electronics may or may not. I certainly wouldn't risk it.

The risk comes when you try to swap from the donor car battery to the dead battery, and the jump leads slip off the terminals before you connect up the original battery. Thus leaving the car with no battery, and probably triggering a spike as the leads disconnect.

It regulates the charge voltage to the battery , however if the battery its not connected the regulator doesnt function correctly and voltage rises

the signwave of the supply produced by the alternator

AC voltage is rms

Domestic supplys are 220volts which is very simply put the average of the voltages supplied by each phase with a 120 degree shift on a signwave , if you could measure each phase individually you would find that it peaks far higher than 220 volts similar princible apply to car alternators

Nope, not anywhere in the EU!

Chris

The average of all 3 phases really ought to be zero...

Cyprus and Poland.

Albania , greece ,bulgaria , hungary , Ireland , poland , portugal all have 220 volt supplies , the old check republic still runs some areas at 120 volts

The EU have 'standardised' all voltages within the EU at 230 volts however they allow a -10 % to a +6% varience to accomadate all the countries at present that means the voltages can be as low as 207 volts or as high as 243.8

All the countries AC is supposed to be 50 cycles but most equipment produced has a tolerence to run at 60 cycles